In a PCM system, an analog input signal is typically applied to an analog-to-digital (A/D) converter for generating a digital code word representing the analog signal. In the A/D converter, the input signal may be connected, for example, through a low-pass filter and a sample-and-hold circuit, to an encoder for generating the digital code word. In normal usage the code word is transmitted in the form of a serial bit stream to a receiving station. Thereat a digital-to-analog (D/A) converter including a decoder reconstructs the original analog signal.
Counting encoders and decoders typically employ a function generator to develop a comparison signal corresponding to a particular companding law. Of increasing interest in the PCM field is the use of segment companding laws, which are essentially piecewise linear approximations of a nonlinear companding law, also called a nonuniform companding law in the art. Each linear piece is called a segment. While at the present time there has been no worldwide standardization of companding laws, two which have been widely used are the .mu. Law and the A Law. For ease of description, the following disclosure is made in terms of the .mu. Law, where the value of .mu. specifies the degree of curvature of the companding characteristic.
Known encoder and decoder function generators typically employ precision components, e.g., a precision resistor ladder, to develop the comparison signal. As a result, if the precision components change nonproportionately, the ratios of successive linear segments may deviate substantially from an intended design ratio. Thereby distortion is introduced in the encoded or decoded PCM signal.
Accordingly, it is a general object of the invention to lessen nonlinear distortion which may be introduced during encoding and decoding of PCM signals.
It is a further object of the invention to lessen the need for precision components and accordingly provide a less expensive digital signal processing arrangement.
A more particular object of the invention is to alleviate the need for precision components in a digital signal processing arrangement for generating a segment companding law comparison signal.